1. Field of the Invention
The present invention relates to a code division multiple access mobile radio communication system and more particularly to increase a cell capacity in a code division multiple access mobile radio communication system. The present invention increases a cell capacity utilizing a gain control of traffic channels by lowering the powers of the traffic channels allocated to a cell to a predetermined level.
2. Description of the Related Art
A maximum forward sector capacity is the maximum capacity at which an adequate quality of speech can be maintained while processing signals for both incoming and outgoing calls. If the load on a sector exceeds the maximum forward sector capacity, the pilot channels allocated in the sector may disappear due to the traffic channels. Moreover, the frame error ratio of the forward sector would increase resulting in a deterioration of the speech quality and/or a disconnection of a call.
The load on the sector which affects the forward sector capacity increases and decreases depending upon the number of calls allocated, speech activity forward traffic channel gains, forward power control subchannel gains, etc. In mobile communication systems, three sectors typically constitute one cell. Accordingly, a forward sector capacity control and a high-power amplifier overload control methods are well known cell capacity control techniques in the related art.
The sector capacity control method controls a sector capacity based upon the number of activated calls being served in the sector. In the sector capacity control method, a service limit threshold value is determined by an experiment in consideration of a sector output, propagation environments, and other factors as determined by the system manager. The service limit threshold value designates the maximum number of calls which can be allocated in the sector. Thus, the total number of calls being served in a sector is compared with the service limit threshold value, and whether to allocate more calls is determined based upon the result of the comparison.
However, sectors have different propagation environments resulting in a different number of calls which can be served in a sector. As a result, the service limit threshold values obtained based upon sector output and propagation environments cannot be reliable for every sector. Thus, the sector capacity control method, based upon the number of activated calls, may sometimes produce an inefficient cell capacity control.
In the high-power amplifier overload control method, the service limit threshold value is determined in consideration of the maximum output of a high-power amplifier which is an output amplifier of the base station. The effective radiated power of the sector at the final output terminal, constantly monitored in the base station, is compared with the service limit threshold value. Then, new calls and handoffs are allowed or limited based upon the result of the comparison.
However, the purpose of the high-power amplifier overload control method is to protect the high-power amplifier rather than to control the sector capacity. Because factors such as the speech quality of a sector, the intensity of the pilot signal, the abnormal release of call caused by an increase of the sector capacity are not considered, the sector capacity may be in saturation before the high-power amplifier becomes overloaded.
Therefore, according to conventional cell capacity control methods as described above, the decrease of the sector capacity due to an increase of subscribers may cause a significant deterioration of the speech quality of a sector. In the worst case, the pilot signal of the sector may disappear and thus the sector may lapse into an unserviceable state.
To improve the reliability of the communication system, a sector capacity control method based upon a call process has been proposed. FIG. 1 shows a block diagram of a base station which performs such a call processing method for the sector capacity control.
The base station of FIG. 1 includes a modular selector/vocoder card (SVC) 1 processing voice data and allocating forward traffic channel powers; a plurality of traffic channel elements 2xcx9c4; and a base station processor (BSP) 5. The SVC 1 allocates traffic channel powers to the plurality of traffic channel elements 2xcx9c4 and the traffic channel elements 2xcx9c4 report the respective power allocation to the BSP 5. The BSP 5 calculates the forward powers of the respective sectors utilizing the traffic channel powers reported by the traffic channel elements 2xcx9c4 and controls its own sector capacity.
FIG. 2 is a flowchart illustrating the call processing method for the sector capacity control, performed by the base station of FIG. 1. First, the forward sector exess capacity value is determined by a ratio of the pilot channel power to the total forward channel power. Then, a call service limit threshold value and a handoff limit threshold value, which are the service limit threshold values, are calculated based on the forward sector exess capacity value.
Particularly, a forward sector exess capacity value at which a maximum number of calls can be serviced while maintaining both a uniform speech quality and powers reserved for handoffs is calculated as the call service limit threshold value. The call service in a sector may be limited due to the call service threshold value, but handoff requests from an adjacent sector can be allowed until the forward sector exess capacity value becomes smaller than the handoff limit threshold value.
Thus, the handoff limit threshold value is smaller than the call service limit threshold value. Also, the fact that the forward sector exess capacity value is equal to or smaller than the handoff limit threshold value means that a sector is currently at the maximum capacity to service normal and handoff calls. The call service limit threshold value and the handoff limit threshold value can be more accurately determined by repeated experiments.
Referring to FIG. 2, a judgement is made whether a service request received from a mobile switching center (MSC) or a mobile station is for a normal call, i.e. origination/terminating or outgoing/incoming call, respectively (S1). If the request is for a normal call, a judgement is made whether to limit the call by comparing the call service limit threshold value with the forward sector exess capacity value (S2). If the request is not for a normal call, the request would be for a handoff and a judgement is made whether to limit the handoff by comparing the handoff limit threshold value with the forward sector exess capacity value (S3).
According to the result of comparison in step S2, the request for normal call is accepted and allocated (S4) or the request is refused (S6). Similarly, according to the result of comparison in step S3, the request for handoff is accepted and allocated (S5) or the request is refused (S7). The call control method estimates the forward power of a sector by utilizing the powers of activated traffic channels allocated to the sector while the base station processes incoming and outgoing calls. As a result, the call control method maintains the forward load of a sector below a predetermined level even if the forward sector capacity is overloaded.
Although the call control method can maintain a uniform speech quality with respect to calls being served in a sector and prevent the decrease of pilot channel power due to the increase of forward power, it still limits the call service requests received after the generation of overload. Thus the method cannot increase a sector capacity. Also, in limiting the calls to maintain the sector capacity, mobile stations in a sector may appear to be in a serviceable state, but may actually be in a state when normal calls and/or the handoff calls cannot be served, thereby causing user inconvenience.
Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art.
An object of the present invention is to allow a more efficient allocation of call requests received in a base station.
Another object of the present invention is to increase a cell capacity. More specifically, an object of the present invention is to increase a cell capacity by a gain control of traffic channels. A cell capacity is increased by lowering the powers of all traffic channels allocated to the cell to a predetermined level.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purposes of the invention, as embodied and broadly described herein, a cell capacity increasing method according to the present invention includes comparing a forward exess capacity value, determined by a ratio of a pilot channel power to the total whole forward channel power, with a sum value of a gain control threshold value and a threshold control value when a normal call is requested in a base station; comparing the forward exess capacity value with the gain control threshold value if it is judged that the forward exess capacity value is smaller than the sum value; and controlling a traffic channel gain by reducing channel powers of traffic channel elements by a predetermined gain control value if it is judged that the forward exess capacity value is smaller than the gain control threshold value.
The forward exess capacity value is determined by an operator of the base station in consideration of the traffic channel elements to which the channel powers are allocated for signal transmission.
Preferably, if the forward exess capacity value is larger than the sum value and the traffic channel elements are already in a gain-controlled state, the gain control to reduce the channel powers of the traffic channel elements is stopped and the gain-controlled state is released. On the other hand, if the forward exess capacity value is larger than the gain control threshold value, the forward exess capacity value is re-calculated and compared with the sum value to repeat the cell capacity increasing process.
Also, after a base station enters a gain-controlled status, it is successively judged whether the forward channel powers are reduced due to a release of incoming or outgoing call requests in the base station. Depending upon the result, the forward exess capacity value is re-calculated and compared with the sum value to repeat the cell capacity i n creasing process.